1. Field of the Invention
The present invention relates to an optical encoder.
2. Related Background Art
For example, an optical encoder described in Japanese Published Examined Patent Application No. H8-10145 is known as a conventional optical encoder. The conventional encoder has an optical scale in which lattice windows having different diffraction patterns are annularly arranged, and diffraction patterns of light to be detected irradiated to the lattice windows through a slit are picked up by an image sensor. The lattice windows are specified from the picked-up diffraction patterns, and also the positions of the lattice windows are specified on the basis of the positions of the diffraction patterns in the image, whereby the absolute angle of a measurement target is detected.